An example of an electrically-controlled unit fuel injector is shown in U.S. Pat. No. 4,392,612 issued to Deckard, et al. on Jul. 12, 1983. In Deckard, et al. the injector includes a mechanically-actuated fuel pumping plunger and an electrically-actuated fuel pressure control valve assembly. The pressure control valve assembly includes a solenoid-operated poppet valve that controls fuel pressure in the unit injector in order to control fuel injection delivery. Fuel pressure is controllably enabled to be developed within the injector by electrical actuation of the pressure control valve valve assembly. Fuel pressure is controllably prevented from developing within the injector by not electrically actuating the pressure control valve assembly.
In such electronically-controlled unit injectors, the armature of the pressure control valve assembly moves the poppet valve in one direction until it engages a valve seat and holds the poppet valve in the fuel sealing position to enable fuel pressure to be developed in the unit injector, eventually resulting in fuel injection. At the end of the fuel injection cycle, the solenoid is electrically deenergized and a return spring backs the poppet valve off of the valve seat and returns the poppet valve to the valve open position which prevents the development of fuel pressure by spilling the fuel back to the fuel reservoir.
Typically, such pressure or spill control valve assemblies use complimentary angled seating surfaces on the poppet valve and the valve seat to achieve the sealing engagement therebetween so as to shut off the fuel.
Several problems have been noted in these presently available pressure control valve assemblies and it is desired to seek solutions thereto. As an example, the sealing engagement of the normally provided angled surfaces between the poppet valve and the seat requires a given pressure which in turn requires that the electrical solenoid coil and the input electrical energy be sufficient to supply the given pressure. Such angled seat configuration also requires a given valve opening force in order to cause the poppet to move so as to thereby disengage the angled surface on the valve member from the angled surface on the valve seat.
If the poppet valve could be made to seat with less than the presently required electromagnetic force, the solenoid coil could be made smaller and require less electrical input energy. Also, the less sealing force required, the coil can be smaller to produce this force. On valve opening, a smaller coil means the coil force decays faster after the coil current shuts off, which means the valve opening starts quicker for a given level of return spring force. Similarly, on the valve opening cycle, if the required sealing force on the poppet could be reduced, then the poppet valve would begin motion more quickly in disengagement from the valve seat which would cause a sharper end of fuel injection. A sharper end of fuel injection is desired so as to provide higher engine thermal efficiency and lower exhaust emissions.
Another problem with presently available pressure control valve assemblies is that they are slow to close because the electromagnetic force produced by the electrical solenoid coil must overcome the return spring force to close the poppet valve. The return spring force is relatively constant during the stroke of the poppet valve and therefore continually opposes the electromagnetic coil force acting to move the poppet valve towards closure.
The present invention is directed to overcoming one or more of the problems as set forth above.